This application claims the priority of Japanese Patent Application No. 3-153526 filed Jun. 25, 1991, which is incorporated herein by reference.
1. Field of the Invention
This invention relates to a drill having a trimming attachment for forming a frusto-conical shaped recess at the opening edge of the hole formed during drilling.
2. Description of the Related Art
FIG. 4 shows a known drill trimming attachment. As seen therein a trimming attachment 33 is attached to the shaft 32 of a drill 31. The trimming attachment 33 consists of a cylindrical body 34 that is clamped to the drill 31 and a trimming blade 36 for trimming the opening edge of a drilled hole 37 to provide a frusto-conical tapered surface 28. The inner surface 35 of the trimming blade 36 abuts against the shaft 32 of the drill, while the base thereof is supported and fixed in the body 34.
Other generally known drills with trimming attachments generally have the drill and the trimming attachment formed as an integral body. Yet another has a trimming blade formed integrally with the bottom of a cylindrical body that is clamped to the drill. When a work piece is drilled using any of these types of drills, the drill can form a hole 37 and also chamfer the opening edge of the hole 37 to provide a frusto conical tapered surface 38.
In the drill with a trimming attachment of the type shown in FIG. 4, the trimming blade 36 is fixed to the shaft 32 of the drill by allowing the inner surface 35 of the trimming blade 36 to abut against the circumference of the shaft 32 and by supporting and fixing the base thereof in the body 34. Accordingly, the tip portion of the trimming blade 36 cannot be secured to the shaft, although the base thereof can be securely fixed. Thus, the trimming blade 36 is sometimes flexed or deflected by the force applied thereto during the chamfering operation. If a work piece is drilled in such state, the work piece suffers a poor appearance at the tapered surface 38, since the opening edge of the hole 37 cannot be chamfered neatly.
On the other hand, drills having a trimming cutter formed integrally therewith, by shaping a piece of bar-like material suffers a problem in that the production cost is high since machining thereof is very difficult. On the other hand, the drill with a trimming attachment of the type having the trimming blade formed integrally with the body 34 at the bottom thereof also suffers a problem in that it requires a number of bodies 34 corresponding to the number of drills with different outer diameters since the outer diameter of the drill which is acceptable in the body 34 is limited, again leading to a high cost of parts.